This invention relates to methods and means for linearizing voltage controlled oscillators.
Voltage controlled oscillators are today commonly used to generate frequency sweep signals wherein the output signal frequency is continuously varied over a selected frequency range as a function of time. For many applications it is important to have the output frequency signals, which commonly are known as chirps, change at a constant, linear rate.
Heretofore, substantial efforts have been made in developing techniques and control systems for linearizing voltage control oscillators. Exemplary of such prior developments are those disclosed in U.S. Pat. Nos. 3,965,438, 3,931,586, 3,916,335, 3,885,138, 3,872,406, 3,669,448, 3,681,706, 3,621,450, 3,585,525 and 3,582,811. In general, the foregoing approaches have involved monitoring of the sweep frequencies of the voltage-controlled oscillator to be linearized, which frequencies are compared with reference sweep frequencies, and the oscillator control signal reshaped through summing and feedback circuitry in response to the detection of actual and reference frequency variations. Recently, as disclosed in U.S. Pat. No. 3,978,411, an open loop feedback concept has been devised which uses a digital memory, a digital-to-analog converter and an integrator in controlling input voltages to the oscillators for preselected discrete frequency selections for television receivers.
Though the just described techniques have linearized voltage controlled oscillators, their degree of success has been limited. Typically, utilization of these prior art methods and systems have achieved linearization in the range of .+-.0.5% with the upper limit being approximately .+-.0.1%. Furthermore, the time involved in performing a linearization operation on individual oscillators has been quite substantial.
Accordingly, it is a general object of the present invention to provide an improved method of linearizing voltage-controlled oscillators.
Another general object of the invention is to provide improved means for linearizing voltage-controlled oscillators.
More specifically, it is an object of the invention to provide a method and means for linearizing voltage-controlled oscillators to a substantially higher degree of linearity than has heretofore been achieved.
Another object of the invention is to provide a method and means for linearizing voltage-controlled oscillators in relatively brief periods of time.